Combustion engine fuel injection apparatus having fluidic control means

ABSTRACT

Fuel injection apparatus for a multicylinder reciprocating engine having a separate fuel injection nozzle connected to supply each cylinder wherein each fuel injection nozzle is supplied an automatically controlled flow of pressurized fuel in response to exhaust gas temperature of the cylinder associated therewith independently of the remaining cylinders by an associated pure fluid amplifier control network to establish optimum fuel-air ration for each cylinder. The pure fluid amplifier control network for each cylinder includes a fixed frequency oscillating fluid amplifier and a bistable fluid amplifier slaved thereto which produces a corresponding fixed frequency pressure pulse output at each of two output ports thereof. One of the two output ports is connected, via passage means exposed to cylinder exhaust gas temperature, to a control input port of a monostable amplifier and the other output port is vented to an opposing control input port thereof such that the phase relationship of the opposing pressure pulses to the control input ports varies as a function of the cylinder exhaust gas temperature. The resulting output pressure derived from the monostable amplifier is applied to a fuel-powered proportional fluid amplifier which proportions fuel flow to the cylinder accordingly.

United States Patent [72] Inventor George R. Howland South Bend, Ind.

[21 Appl. No. 840,293

[22] Filed July 9, 1969 [45] Patented Apr. 27, 1971 [73] Assignee The Bendix Corporation [54] COMBUSTION ENGINE FUEL INJECTION APPARATUS HAVING FLUIDIC CONTROL MEANS 12 Claims, 4 Drawing Figs.

Primary Examiner-Laurence M. Goodridge Attorneys--Gordon I-I. Chenez and Plante, Arens, I-Iartz, Hix

and Smith ABSTRACT: Fuel injection apparatus for a multicylinder reciprocating engine having a separate fuel injection nozzle connected to supply each cylinder wherein each fuel injection nozzle is supplied an automatically controlled flow of pressurized fuel in response to exhaust gas temperature of the cylinder associated therewith independently of the remaining cylinders by an associated pure fluid amplifier control network to establish optimum fuel-air ration for each cylinder. The pure fluid amplifier control network for each cylinder includes a fixed frequency oscillating fluid amplifier and a bistable fluid amplifier slaved thereto which produces a corresponding fixed frequency pressure pulse output at each of two output ports thereof. One of the two output ports is connected, via passage means exposed to cylinder exhaust gas temperature, to a control input port of a monostable amplifier and the other output port is vented to an opposing control input port thereof such that the phase relationship of the opposing pressure pulses to the control input ports varies as a function of the cylinder exhaust gas temperature. The resulting output pressure derived from the monostable [56] References Cited amplifier is applied to a fuel-powered proportional fluid UNITED STATES PATENTS amplifier which proportions fuel :flow to the cylinder 2,244,669 6/1941 Becker 123/l40.3 accordingly.

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EXHAUST All? IN COMBUSTION ENGINE FUEL INJECTION APPARATUS HAVING FLUIDIC CONTROL MEANS BACKGROUND OF THE INVENTION The exhaust gas temperature of a reciprocating engine is the temperature of combustion products discharged from the cylinder or cylinders of the engine. It is a well-known practice to employ engine analyzer equipment to monitor the exhaust gas temperature of each cylinder of a multicylinder engine. A widespread in the sensed temperatures of the cylinders provides an indication of the relative perfon'nance of each cylinder. Assuming that each cylinder operates with substantially the same fuel-air ratio, a high cylinder exhaust gas temperature indicates cylinder exhaust valve leakage whereas a relatively low cylinder exhaust gas temperature indicates piston ring leakage and/or fouled ignition. It will be recognized that such engine analyzer equipment provides an adequate indication of engine cylinder performance but does not provide automatic control of fuel and thus fuel-air ratio to any given one or more defective cylinders to compensate the condition. In most cases, the engine operator has to exercise manual control over the engine fuel control system to suitably modify fuel flow in an attempt to improve conditions of the defective cylinder at the expense of reducing the efficiency of the remaining cylinders.

It has been observed from test operation with a multicylinder reciprocating engine that a unique relationship exists between engine cylinder fuel-air ratio and cylinder exhaust gas temperature which is independent of engine power output over a wide range of engine power output. Such text operation substantiates theoretical considerations which indicate that the ratio of exhaust gas temperature to engine ambient or supply air temperature is a direct function of the fuel-air ratio. Since the primary purpose of a reciprocating engine fuel control is to exercise control over the fuel-air ratio of the induction mixture to the engine cylinders, modulation of fuel flow to the engine cylinders to maintain a desired exhaust gas temperature will fulfill that objective.

A fuel control which automatically controls fuel flow individually to each cylinder of a multicylinder engine to maintain cylinder exhaust gas temperature at a desired value provides a number of advantages. Since fuel flow is based on cylinder exhaust gas temperature, variations in fuel injection nozzle size of the engine cylinders and/or unfavorable air and fuel distribution characteristics of the induction manifold system to the cylinders have substantially no adverse effect on overall engine performance. Furthermore, cylinder spark plug fouling normally causes incomplete combustion which in turn, aggravates the fouling condition. Automatic control of fuel flow on the basis of cylinder exhaust gas temperature will effect a reduction in fuel to the fouled plug which results in a self-cleaning effect on the fouled plug. It will be recognized that exhaust valve leakage normally results in exposure of the valve stem to excessive temperature producing possible valve failure. Automatic control of fuel flow in response to the relatively high cylinder exhaust gas temperature will provide a richer fuel-air ratio to the cylinder having the leaking exhaust valve to reduce the exhaust gas temperature thereof tending to avoid the potential valve failure.

A fuel control operative to automatically control fuel flow in the above-mentioned manner in response to individual cylinder exhaust gas temperature would require a complex arrangement of conventional mechanical and/or electronic hardware which tends to make such a control prohibitive from a cost standpoint. Furthermore, since size, weight, reliability and maintenance suffers in proportion to the complexity of control mechanism involved, such a mechanical or electronic fuel control may not be desirable.

In relatively recent years, fluidic devices such as pure fluid amplifiers have been developed having no moving parts and which are reliable and accurate, relatively inexpensive, sturdy, and compact and perform control functions equivalent to conventional mechanical and/or electronic element control functions. Fluidic devices are ideally suited for application to a control system embodying the above-mentioned concept of controlling fuel flow to each individual cylinder of a multicylinder engine as a function of the cylinder exhaust gas temperature.

It is an object of the present invention to provide a piston engine fuel control having pure fluid control network apparatus for automatically controlling fuel flow to an individual engine cylinder in response to that cylinders exhaust gas temperature.

It is another object of the present invention to provide a multicylinder piston engine fuel control operative to automatically control fuel flow to each engine cylinder in response to the associated cylinder exhaust gas temperature independently of the remaining engine cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a multicylinder piston engine and fuel control system therefor embodying the present invention;

FIG. 2 is a schematic representation of a pure fluid amplifier control network for controlling fuel flow to one engine cylinder of the multicylinder engine of FIG. 1 with the similar control networks for the remaining cylinders shown in block form;

FIG. 3 is a section view taken on line 3-3 of FIG. 1;

FIG. 4 is a section view taken on line 44 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, numeral 20 designates a conventional piston engine having a plurality of cylinders, not shown, which may number more or less than the three represented in block form as, for example, in the case of a sixcylinder engine. Each cylinder is: provided with an air induction pipe 22 leading to the cylinder inlet valve, not shown, and connected to a common air manifold 24 having an air inlet 26. A movable throttle valve 28 suitably connected to air inlet 26 and an operator-actuated control member, in part represented by lever 30, is adapted to control the effective flow area of inlet 26 and thus mass airflow to the engine cylinders. Each cylinder is further provided with an exhaust pipe or stack 32 connected to the exhaust valve, not shown, thereof.

Each cylinder air induction pipe 22 is supplied a controlled flow of fuel via fluidic control apparatus generally indicated in block form by 34 in FIG. 1 which represents a preferred T- shaped package as will be discussed hereinafter. Each block 34 is connected adjacent associated exhaust and induction pipes 32 and 22, respectively, by suitable support means, not shown, and is provided with an outwardly extending fuel injection nozzle 38 and passage member 40 (see FIG. 4). The fuel injection noule 38 extends through an opening 42 in air induction passage 22 and is adapted to inject pressurized fuel therein. The passage member 40 extends through a suitable opening 44 in exhaust pipe 32 and is exposed to the flow of hot motive exhaust gas therein.

The blocks 34 are each supplied pressurized fuel at pressure P, via a fuel tank 46, a fuel conduit 48 containing a fuel pump 50 suitably driven by the engine 20 or independently operable electric motor means, not shown, an operator-actuated fuel shutoff valve 52, and a passage 54.. A passage 56 and fuel return conduit 58 communicates each block 34 with fuel conduit 48 at relatively low pressure P upstream from pump 50. Each block 34 is further vented via a passage 60 and conduit 62 to a subatrnospheric air pressure source P, of approximately 2 to 3 p.s.i. below atmospheric pressure such as vacuum pump 64 which may be driven by the engine 20 or suitable independently operable motor means, not shown.

A manifold air pressure-sensitive fluidic device generally indicated by 66 is vented via a passage 68 and an opening 70 in manifold 24 to manifold air pressure P,,, downstream from throttle valve 28. A fluidic output signal is transmitted from fluidic device 66 to each of the blocks 34 via a passage 72 and associated branch passages 74. A passage 76 vents fluidic device 66 to passage 62 at subatrnospheric pressure P,,.

A fluid pressure signal-generating fluidic device generally indicated by 78 is vented via a passage 80 to passage 62, and to each of the blocks 34 via a passage 82 and associated branch passages 84. A position input signal representing lever 30 position is impressed on fluidic device 78 via a link 86.

Referring to FIG. 2, the fluidic control apparatus designated by one block 34 is shown in circuit form. It will be understood that the other blocks 34 corresponding to the remaining five engine cylinders contain duplicate fluidic control apparatus circuitry and therefore need not be shown. The various pure fluid amplifier devices per se which together make up the circuit shown are prior art structure and are shown therefore in conventional schematic form.

FIG. 2 shows a bistable pure fluid amplifier 88 of the oscillator type having an inlet 90 vented to atmospheric air at pressure P, and output passages 92 and 94 vented to passage 60 at relatively lower air pressure P,,. Feedback passages 96 and 98 preferably of equal length connect output passages 92 and 94 with opposed control input ports 100 and 102, respectively, which ports are adapted to inject air transversely against the power air jet passing therebetween to alternately deflect the same to output passages 92 and 94. The amplifier 88 is exposed to ambient or atmospheric air at pressure P such that the speed of a pressure pulse passing through feedback passages 96 and 98 varies as a function of ambient or atmospheric air temperature as will be recognized by those persons skilled in the art.

A bistable pure fluid amplifier 104 has an inlet 106 vented to atmospheric air at pressure P, and output passages 108 and 110 vented to passage 60 at relatively lower air pressure P,,. Opposed control ports 112 and 114 are vented via passages 116 and 118 to feedback passages 96 and 98, respectively, thereby slaving amplifier 104 to amplifier 88 to produce output pressure pulsations of the same frequency at both amplifiers.

A monostable pure fluid amplifier 120 has an inlet 122 vented to atmospheric air at pressure P, and output passages 124 and 126 vented to passage 60 at relatively lower air pressure P,,. Opposed control ports 128 and 130 are vented to output passages 108 and 110, respectively, of amplifier 104 via conduit 132 and passage 134. The conduit 132 is partially defined by passage 40 exposed to exhaust. gas and the remaining portion thereof is exposed to ambient or atmospheric air at temperature T which remaining portion is of the same length as passage 134 also exposed to ambient air atmospheric air at temperature T,,.

A fuel-powered proportionally acting pure fluid amplifier 136 has an inlet 138 vented to fuel conduit 48 via passage 54 and output passages 140 and 142. Output passage 140 is vented to fuel return passage 56 and output passage 142 is vented to fuel injection nozzle 38. Control port 144 communicates with a passage 146 intermediate two series flow restrictions 148 and 150 therein which passage 146 is connected at one end to output passage 126 of amplifier 128 and at the opposite end to passage 60 at relatively low air pressure P,,. A passage 147 communicates output passage 124 with relatively low air pressure P, and is provided with series restrictions 149 and 151 equivalent to restrictions 148 and 150 of passage 146. Control port 152 opposing control port 144 is vented via passages 72 and 74 to one of two output passages 156 and 158 of a proportionally acting pure fluid amplifier 168 which passages 156 and 158 communicate with passage 60.

Amplifier 160 is provided with an inlet port 162 vented to atmospheric air at pressure P, and opposed control ports 164 and 166 which are vented to passages 168 and 170, respectively, intermediate associated series flow restrictions 172, 174 and 176, 178 disposed in passages 168 and 170, respectively. A chamber 180 of predetermined volume is vented to passage 168 intermediate restrictions 172 and 174.

Passages 168 and 170 are in parallel flow arrangement and are vented at one end to inlet port 162 at air pressure P and at the opposite end to passage 68 at relatively lower manifold air pressure P in manifold 24.

The fluid pressure signal-generating device 78 includes a passage 182 having series flow restrictions 184 and 186 disposed therein and vented at opposite ends to atmospheric air pressure P and passage 60 at relatively lower air pressure P,,. A passage 188 in parallel flow relationship with restriction 184 is provided with a restriction 190 and movable valve 192 in series flow therein. The passage 182 intermediate restrictions 184 and 186 is vented via passage 82 to passage OPERATION it will be assumed that the engine 70 is operating at a given output speed or power condition corresponding to the setting of the throttle valve 28 as established by control lever 30 which occupies a position corresponding to either engine idle or maximum power in which case a relatively rich fuel-air ratio is desired to reduce the engine cylinder operating temperature and thus avoid engine overheating.

The oscillator bistable amplifier 88 is powered by the air pressure difierential P P,, imposed thereon and the resulting power air jet is alternately deflected to output passages 92 and 94 at a frequency dependent upon the length of feedback passages 96 and 98 as well as the temperature, T of the ambient or atmospheric air to which the passages 96 and 98 are exposed. To that end, deflection of the power air jet to one of its two stable positions pressurizes output passage 94 and thus feedback passage 98 and control port 102 connected thereto which, in turn, overcomes the latching effect imposed on the power air jet causing the same to deflect to its opposite stable position whereupon output passage 92 and thus feedback passage 96 and control port connected thereto is pressurized thereby again unlatching the power air jet and deflecting the same back to output passage 94. The alternate pressurization of output passages 92 and 94 is continuous as long as the power air jet flow exists thereby producing a series of pressure pulses at each output passage 92 and 94 having the same frequency. it will be recognized that the time for a pressure pulse to travel through feedback passage 96 or 98 varies directly with the length thereof and inversely with the temperature of the ambient or atmospheric air to which the passages 96 and 98 are exposed. The pulse frequency, in turn, varies directly with ambient or atmospheric temperature and inversely with the total length of the two feedback passages 96 and 98.

The pressure pulses derived from output passages 92 and 94 of amplifier 88 are transmitted via passages 116 and 118 to control ports 112 and 114, respectively, of bistable amplifier 104 which, like amplifier 88, is powered by the air pressure differential P,,P,, imposed thereon. The power air jet of amplifier 104 deflects in response to the alternate pressurization of control ports 112 and 114 and produces alternate pressurization of output passages 108 and thereby generating a series of output pressure pulses at each of the output passages 108 and 110 having a frequency corresponding to that of the output pressure pulses occurring at amplifier 88.

The pressure pulses generated at output passages 108 and 110 are transmitted through conduit 132 and passage 134 to control ports 128 and 130, respectively, of monostable amplifier which, like amplifiers 88 and 104, is powered by the air pressure differential P,,P,, imposed thereon. The speed at which a pressure pulse travels through conduit 132 is dependent upon the temperature of the air therein and varies therefore as a function'of exhaust gas temperature, T,.;, to which the passage portion 40 of conduit 132 is exposed and ambient or atmospheric temperature, T,,, to which the remaining portion of conduit 132 is exposed. The speed of a pressure pulse passing through passage 134 varies as a function of ambient or atmospheric air temperature, T,,, to which passage 134 is exposed. By design, the lengths of conduit 132 and passage 134 exposed to temperature T are made equal such that the time differential between pressure pulses arriving at control port 128 and 130 varies as a function of the exhaust gas temperature, T,;, imposed on passage portion 40 of conduit 132. It will be understood that a pressure pulse occurring at output passage 110 of amplifier 104 is 180 out of phase with a subsequent pressure pulse at output passage 108 such that the total phase shift, 9, of the resulting pressure pulses occurring at control ports 122 and 128 is defined by the relationship:

=180+360CLVQ E wherein L represents the length of passage 40, T represents ambient temperature, T represents cylinder exhaust gas temperature and C is a well-known constant.

The power air jet of monostable amplifier 120 is deflected to output passage 126 in response to the pressure pulses occurring at control ports 128 and 130 in accordance with the above-identified phase relationship therebetween thereby establishing pressure or flow in output passage 126 which is directly proportional to the phase shift and thus ratio of ambient and exhaust gas temperatures, T,, and T The restrictions 148 and 150 serve to attenuate the output pulse frequency generated at output passage 126 thereby establishing a relatively stable pressure which is transmitted to control port 144 of fuel-powered proportional amplifier 136 where it acts against the fuel jet in opposition to an opposing reference pressure at control port 152 corresponding to a desired reference exhaust gas temperature, T

The reference pressure established at control port corresponds to a desired relatively low cylinder exhaust gas temperature. It will be recognized that at engine idle operation, particularly in the case of air-cooled engines, cooling airflow is at a minimum and engine cylinder operating temperatures should be reduced accordingly to avoid subjecting the engine to undesired overheating. Also, at maximum power operation, the engine may be subject to overheating in which case it is desirable to reduce cylinder operating temperatures by providing a rich fuel-air ratio mixture to the engine cylinders. To that end, the valve 192 occupies a closed position in response to control lever 30 position requesting engine idle or maximum power. The air pressure-generated intermediate restrictions 184 and 186 is a predetermined function of the fixed area ratio thereof and is transmitted via passages 72 and 74 to control port 152 where the resulting pressure differential between it and the opposing pressurized control port 144 represents the error between reference and actual cylinder exhaust gas temperature. At zero temperature error, the opposing pressures at control ports 144 and 152 are equal and the fuel jet is separated into two flow paths one of which is through output passage 142 to injection nozzle 38 and the other through output passage 140 to the inlet of fuel pump 50. In the event that the pressure signal at control port 144 overcomes that at control port 152 as a result of an excess cylinder exhaust gas temperature, the fuel jet is deflected toward output passage 142 thereby increasing the quantity of fuel directed to injection nozzle 38 which, for a constant cylinder airflow, results in a richer fuelair ratio mixture to the cylinder and a corresponding reduction in cylinder exhaust gas temperature. A temperature error in the opposite sense results in deflection of the fuel jet toward output passage 140 which, in turn, decreases the quantity of fuel directed to injection nozzle 38 to cause a corresponding leaner fuel-air ratio mixture and thus increase cylinder exhaust gas temperature. it will be recognized that the above-described control over-fuel flow to maintain cylinder exhaust gas temperature substantially constant at a predetermined value is effective regardless of changes in airflow to the engine cylinder at any given fuel flow supplied thereto since the sensed exhaust gas temperature, T tends to increase with a reduced fuel-air ratio caused by increased airflow and decrease with an increased fuel-air ratio caused by decreased airflow.

The reference temperature, T air pressure signal applied to control port 152 is varied in response to movement of control lever 30 to an engine power position intermediate idle and maximum as, for example, that corresponding to cruise operation, in which case fuel flow is regulated to establish optimum fuel economy. To that end, movement of control lever 30 to the cruise engine power position resets the throttle valve 28 accordingly and, at the same time, actuates valve 192 to an open position thereby establishing an increase in air pressure intermediate restrictions 184 and 186, by virtue of the effective flow area of restriction 190 which is additive to parallel restriction 184. The corresponding increased air pressure established at control port 152 represents a modified reference temperature, T,,, and biases the fuel jet toward output passage in opposition to the existing opposing pressure at control port 144.

The simultaneous increase in airflow to the engine cylinder resulting from opening movement of throttle valve 28 tends to reduce the fuel-air ratio as mentioned heretofore whereupon cylinder exhaust gas temperature, T increases accordingly causing a corresponding increasing in pressure at control port 144. The sensed exhaust gas temperature, T and thus air pressure at control port 144 increases to the extent required to equal the reference temperature and thus air pressure at control port 152 thereby stabilizing the fuel jet and thus quantity of fuel delivered to output passage 142 and fuel injection nozzle 38. Any tendency for the sensed exhaust gas temperature, T to increase or decrease from the reference temperature established by the air pressure at control port 144 results in a corresponding deflection of the fuel jet toward or away from output passage 142 to reduce or increase the fuelair ratio in the heretofore-mentioned manner thereby controlling the exhaust gas temperature, T to the reference temperature value.

It is recognized that sudden opening movement of throttle valve 28 in response to control lever 30 may cause an initial fuel deficiency tending to cause hesitation in engine response. Such a problem may be eliminated by the manifold airpressure-sensitive device 66. For example, opening throttle valve 28 and the resulting increase in airflow to the engine cylinder may result in a substantial excess of air for the existing fuel flow supplied injection nozzle 38 thereby adversely affecting the cylinder combustion process. Opening throttle valve 28 produces a corresponding increase in manifold 24 air pressure P which is transmitted to passages 168 and 170 of device 66 thereby causing a simultaneous rise in air pressure intermediate restrictions 172 and 174. Likewise, the air pressure intermediate restrictions 176 and 178 rises but with a transient lag relative to the increased pressure between restrictions 172 and 174 by virtue of the volume of chamber which lag is proportional to the rate of change of the manifold air pressure P The resulting transient pressure differential generated between control ports 164 and 166 deflects the power air jet passing therebetween toward output passage 156 thereby reducing the airflow to and/or pressure in output passage 158 which, in turn, causes a corresponding pressure decrease in passages 72 and 74 leading to control port 152 of which fuel-powered amplifier 136 thereby providing a temporary bias to the reference temperature pressure input signal. The resulting deflection of the fuel jet toward output passage 142 produces a corresponding increase in fuel flow to fuel injection nozzle 38 thereby compensating for the increased airflow through throttle valve 28 to the engine cylinder. As the manifold air pressure P stabilizes, the air pressure intermediate the restrictions 176 and 178 and air pressure intermediate restrictions 172 and 174 equalize whereupon the power air jet of amplifier 166 assumes its normal nondeflected position causing the pressure in output passage 158 to increase accordingly, thereby reestablishing the normal pressurization of control port 152 corrfihding to the desired reference temperature. It will be recognized that the above-described control of fuel flow as a function of the rate of change of manifold air pressure P is reversed when throttle valve 28 is moved to reduce airflow through manifold 24 in which case the resulting drop in manifold air pressure P has the affect via its eflect on amplifier 160 of temporarily biasing the reference temperature pressure signal at control port 152 to reduce fuel flow to the fuel injection nozzle 38.

The valve 192 has been described as a two-position valve depending upon the position of control lever 30. However, it is recognized that the valve 192 may take the form of a conventional variable area valve actuated by various parameters of operation other than the position of control lever 30 in which case the reference pressure generated intermediate restrictions 184 and 186 can be varied as a predetermined function of one or more selected parameters of engine operation.

The fluidic amplifiers 88, 104, 120 and 136 may be assembled and suitably encased in a conventional manner to define the T-shaped construction shown in FIGS. 1, 2, and 3. The various portions of the control circuitry such as amplifier 88 which are to be maintained at ambient or atmospheric air temperature, T,,, may be contained in the leg portion of the T- shape which has its major portion exposed to the flow of ambient or atmospheric air adjacent the engine 20.

I claim:

1. Fuel control apparatus for a multicylinder reciprocating engine having an inlet pipe for conducting a fuel-air mixture to each cylinder and an exhaust pipe for conducting exhaust gas from each cylinder, said fuel control apparatus comprising:

a plurality of pure fluid amplifier means each of which is connected to an associated one of the engine cylinders and responsive to a variable condition of the exhaust gas of said one cylinder for generating a fluid pressure signal which varies-as a function of said exhaust gas condition; and

fuel control means operatively connected to supply fuel to the inlet pipe of said one cylinder and responsive to said fluid pressure signal for controlling fuel flow to and thus fuel-air ratio of said one cylinder independently of the remaining cylinders.

2. Fuel control apparatus as claimed in claim 1 wherein:

said exhaust gas condition is exhaust gas temperature:

3. Fuel control apparatus as claimed in claim Z'Wherein the inlet pipe to each cylinder is connected to a controllable air supply; and wherein each of said plurality of pure fluid amplifier means is further responsive to supply air temperature and operative to generate a fluid pressure signal which varies as a function of cylinder exhaust gas temperature and supply air temperature.

4. Fuel control apparatus as claimed in claim 3 wherein:

each of said pure fluid amplifier means includes;

first fluidic amplifier means operative to generate first and second series of fluid pressure pulses having a common frequency;

second fluidic amplifier means;

first conduit means connected to transmit said first series of pressure pulses from said first amplifier means to said second amplifier means;

second conduit means having a portion of the length thereof exposed to the exhaust gas flow through the exhaust pipe of said one cylinder and connected to transmit said second series of pressure pulses from said first amplifier means to said second amplifier means;

said second amplifier means being responsive to said first and second series of pressure pulses and operative to generate said fluid pressure signal which varies. in response to the phase shift between said first and second series of pressure pulses as a function of said cylinder exhaust gas temperature;

means for generating a reference fluid pressure corresponding to a predetermined desired cylinder exhaust gas temperature;

said fuel control means is connected to respond to said fluid pressure signal which varies as a function of cylinder exhaust gas temperature and said reference fluid pressure for controlling fuel flow in response to an error between actual and desired cylinder exhaust gas temperatures.

5. Fuel control apparatus as claimed in claim 4 wherein:

said first conduit means is exposed to supply air temperature;

said second conduit having said portion of its length exposed to cylinder exhaust gas temperature and the remaining portion of the length thereof exposed to supply air temperature;

said first conduit means and said portion of said second conduit means exposed to supply air temperature being of equal length;

said fluid pressure signal derived from said second amplifier means being defined by a series of fluid pressure pulses having a pulse duration proportional to the ratio of cylinder exhaust gas temperature and supply air temperature.

6. Fuel control apparatus as claimed in claim 4 wherein:

said first fluidic amplifier means includes an oscillator fluidic amplifier having a power air jet and first and second output passages and control means for deflecting said power air jet to alternately pressurize said first and second output passages;

a bistable fluidic amplifier having a power air jet and third and fourth output passages and responsive to said first and second series of pressure pulses which deflect the power air jet thereof to alternately pressurize said third and fourth output passages thereby generating said first and second series of pressure pulses, respectively;

said second fluidic amplifier means includes a monostable fluidic amplifier having a power air jet and fifth and sixth output passages and responsive to said first and second series of pressure pulses for deflecting said power jet thereof from a stable position whereby said power air jet is directed to said fifth output passage to a nonstable position whereby said power air jet is directed to said sixth output passage;

said fluid pressure signal being derived from said sixth output passage.

7. Fuel control apparatus as claimed in claim 6 and further including:

air flow restricting means operatively connected to said sixth output passage for attentuating pressure pulses in said fluid pressure signal to provide a substantially constant fluid pressure.

8. Fuel control apparatus as claimed in claim 4 wherein:

said reference fluid pressure is derived from a first passage connecting a first source of pressurized air with a second source of air at relatively lower pressure and provided with first and second air flow restrictions in series flow relationship therein;

said reference fluid pressure being generated intermediate said first and second restrictions and varying depending upon the area ratio thereof.

9. Fuel control apparatus as claimed in claim 8 and further including:

a second passage connected to said first passage in parallel flow relationship with said first restriction;

valve means in said second passage for varying the effective flow area thereof to vary the effective flow area ratio relationship between said first and second restrictions and thus said reference fluid pressure accordingly; and

control means for actuating said valve means.

10. Fuel control apparatus as claimed in claim 1 and further including:

control means for generating a reference fluid pressure corresponding to a predetermined desired value of said variable condition of exhaust gas operatively connected to said fuel control means to impose said reference fluid pressure thereon;

said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure thereon;

said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure for controlling fuel flow to said one cylinder to maintain said variable condition of exhaust gas substantially constant at said predetermined desired value.

ll. Fuel control apparatus as claimed in claim and further including:

second control means responsive to a variable condition of engine operation and operatively connected to said fuel control means for temporarily modifying said reference fluid pressure in response to a predetermined variation in said condition of engine operation.

12. Fuel control apparatus as claimed in claim 3 wherein said controllable air supply includes an air manifold having a positionable air throttle valve operatively connected thereto and said fuel control apparatus further includes:

first control means for generating a reference fluid pressure corresponding to a predetermined desired value of said exhaust gas temperature and operatively connected to said fuel control means for imposing said reference fluid pressure thereon; said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure for controlling fuel flow to said one cylinder to maintain said exhaust gas temperature substantially constant at said predetermined desired value; and second control means responsive to the manifold air pressure and operatively connected to said fuel control means for temporarily modifying said reference fluid pressure in response to the rate of change of manifold air pressure caused by movement of said air throttle valve. 

1. Fuel control apparatus for a multicylinder reciprocating engine having an inlet pipe for conducting a fuel-air mixture to each cylinder and an exhaust pipe for conducting exhaust gas from each cylinder, said fuel control apparatus comprising: a plurality of pure fluid amplifier means each of which is connected to an associated one of the engine cylinders and responsive to a variable condition of the exhaust gas of said one cylinder for generating a fluid pressure signal which varies as a function of said exhaust gas condition; and fuel control means operatively connected to supply fuel to the inlet pipe of said one cylinder and responsive to said fluid pressure signal for controlling fuel flow to and thus fuel-air ratio of said one cylinder independently of the remaining cylinders.
 2. Fuel control apparatus as claimed in claim 1 wherein: said exhaust gas condition is exhaust gas temperature.
 3. Fuel control apparatus as claimed in claim 2 wherein the inlet pipe to each cylinder is connected to a controllable air supply; and wherein each of said plurality of pure fluid amplifier means is further responsive to supply air temperature and operative to generate a fluid pressure signal which varies as a function of cylinder exhaust gas temperature and supply air temperature.
 4. Fuel control apparatus as claimed in claim 3 wherein: each of said pure fluid amplifier means includes; first fluidic amplifier means operative to generate first and second series of fluid pressure pulses having a common frequency; second fluidic amplifier means; first conduit means connected to transmit said first series of pressure pulses from said first amplifier means to said second amplifier means; second conduit means having a portion of the length thereof exposed to the exhaust gas flow through the exhaust pipe of said one cylinder and connected to transmit said second series of pressure pulses from said first amplifier means to said second amplifier means; said second amplifier means being responsive to said first and second series of pressure pulses and operative to generate said fluid pressure signal which varies in response to the phase shift between said first and second series of pressure pulses as a function of said cylinder exhaust gas temperature; means for generating a reference fluid pressure corresponding to a predetermined desired cylinder exhaust gas temperature; said fuel control means is connected to respond to said fluid pressure signal which varies as a function of cylinder exhaust gas temperature and said reference fluid pressure for controlling fuel flow in response to an error between actual and desired cylinder exhaust gas temperatures.
 5. Fuel control apparatus as claimed in claim 4 wherein: said first conduit means is exposed to supply air temperature; said second conduit having said portion of its length exposed to cylinder exhaust gas temperature and the remaining portion of the length thereof exposed to supply air temperature; said first conduit means and said portion of said second conduit means exposed to supply air temperature being of equal length; said fluid pressure signal derived from said second amplifier means being defined by a series of fluid pressure pulses having a pulse duration proportional to the ratio of cylinder exhaust gas temperature and supply air temperature.
 6. Fuel control apparatus as claimed in claim 4 wherein: said first fluidic amplifier means includes an oscillator fluidic amplifier having a power air jet and firSt and second output passages and control means for deflecting said power air jet to alternately pressurize said first and second output passages; a bistable fluidic amplifier having a power air jet and third and fourth output passages and responsive to said first and second series of pressure pulses which deflect the power air jet thereof to alternately pressurize said third and fourth output passages thereby generating said first and second series of pressure pulses, respectively; said second fluidic amplifier means includes a monostable fluidic amplifier having a power air jet and fifth and sixth output passages and responsive to said first and second series of pressure pulses for deflecting said power jet thereof from a stable position whereby said power air jet is directed to said fifth output passage to a nonstable position whereby said power air jet is directed to said sixth output passage; said fluid pressure signal being derived from said sixth output passage.
 7. Fuel control apparatus as claimed in claim 6 and further including: air flow restricting means operatively connected to said sixth output passage for attentuating pressure pulses in said fluid pressure signal to provide a substantially constant fluid pressure.
 8. Fuel control apparatus as claimed in claim 4 wherein: said reference fluid pressure is derived from a first passage connecting a first source of pressurized air with a second source of air at relatively lower pressure and provided with first and second air flow restrictions in series flow relationship therein; said reference fluid pressure being generated intermediate said first and second restrictions and varying depending upon the area ratio thereof.
 9. Fuel control apparatus as claimed in claim 8 and further including: a second passage connected to said first passage in parallel flow relationship with said first restriction; valve means in said second passage for varying the effective flow area thereof to vary the effective flow area ratio relationship between said first and second restrictions and thus said reference fluid pressure accordingly; and control means for actuating said valve means.
 10. Fuel control apparatus as claimed in claim 1 and further including: control means for generating a reference fluid pressure corresponding to a predetermined desired value of said variable condition of exhaust gas operatively connected to said fuel control means to impose said reference fluid pressure thereon; said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure thereon; said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure for controlling fuel flow to said one cylinder to maintain said variable condition of exhaust gas substantially constant at said predetermined desired value.
 11. Fuel control apparatus as claimed in claim 10 and further including: second control means responsive to a variable condition of engine operation and operatively connected to said fuel control means for temporarily modifying said reference fluid pressure in response to a predetermined variation in said condition of engine operation.
 12. Fuel control apparatus as claimed in claim 3 wherein said controllable air supply includes an air manifold having a positionable air throttle valve operatively connected thereto and said fuel control apparatus further includes: first control means for generating a reference fluid pressure corresponding to a predetermined desired value of said exhaust gas temperature and operatively connected to said fuel control means for imposing said reference fluid pressure thereon; said fuel control means being responsive to the relative error between said fluid pressure signal and said reference fluid pressure for controlling fuel flow to said one cylinder to maintain said exhaust gas temperature substantiallY constant at said predetermined desired value; and second control means responsive to the manifold air pressure and operatively connected to said fuel control means for temporarily modifying said reference fluid pressure in response to the rate of change of manifold air pressure caused by movement of said air throttle valve. 